To some extent that depends on the size of the toilet. I'd hesitate to use this method on a cat weighing less than five pounds or so, for fear of causing plumbing problems. At the vet's office yesterday I met a woman who had a 29-pound Maine coon cat; I don't think I'd want to try it with him. And I've hesitated to use it on my 15-pound Siamese-Himalayan mix, Yehudi; he's got so much fur that I'm afraid it might clog the trap. His smaller, shorter-haired sister, Hepzibah, might be a good subject for experimentation, though I haven't been able to talk her into trying it yet.
Generally, though, I think the system will work pretty well on short-to-medium-hair cats between six and 15 pounds. I'd suggest a ratio of about two ounces of shampoo per pound of cat.
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